Masks are used at various stages in semiconductor processing and packaging to form patterns on various types of substrates. For instance, masks of various materials (e.g. metal, quartz etc.), sizes and types may be used in conjunction with photosensitive materials to expose and form semiconductor devices in a semiconductor substrate. Masks may be used to form interconnections between semiconductor devices. Additionally, masks are commonly used to form interconnection patterns used to connect integrated circuits to packaging substrates. For example, masks are commonly used to form controlled collapse chip contacts ("C4") on semiconductor wafers for making connection between an integrated circuit chip and a ceramic substrate.
Defects on the surface of a mask can arise during mask fabrication or subsequent handling. Such defects generally take the form of non-planar areas (e.g. "high spots") or other irregularities on the generally flat surface of the mask. The defects can cause a variety of problems. For example, if the "high spot" flakes off the mask and lodges in the surface of a semiconductor wafer, it may cause an immediate or future accidental electrical short, particularly if the mask is metal. Or, a defect may scratch the wafer, resulting in physical damage that can also be manifested by functional or reliability failures. In addition, non-planar masks (e.g. masks which do not have a uniform thickness across their surface area) can cause inaccuracies in patterning.
Because of the difficulties created by defects on the mask surface, great care is taken to avoid or minimize the occurrence of the defects. Masks are carried in protective containers designed to avoid damage to the masks and are carefully inspected after fabrication and after each use to identify defects so that the defective masks are not used to process semiconductor wafers. While this practice helps to avoid the defective masks from contaminating or otherwise damaging wafers, it results in unacceptable waste of the defective masks. What is needed is a method to repair the defective masks, so that they may be re-used without causing damage or contamination to the underlying substrate to be processed.